A drilling machine has the disadvantage of producing long chips which present various problems in the drilling operation because they are difficult to move quickly away from the work zone and may impair the quality of the surface of the hole produced.
One remedy to this disadvantage is to cause these chips to break up by varying their thickness and by repeatedly interrupting the cutting operation. This is achieved by applying to the cutting tool, which is generally a drill bit, an axial vibration which makes the feedrate (the rate of penetration into the material) cyclically variable and therefore makes the thickness of the chip variable, with amplitudes and frequencies that cause the chips to break up.
At the same time, there are drilling operations in which it is beneficial to vibrate the tool only at certain times (when drilling multilayer materials for example) or to change the amplitudes and/or the frequencies of the oscillations in real time (in order to react and to adapt the cutting process to suit the material being drilled for example). It is therefore necessary to have a device that can be controlled, with sufficiently rapid reaction and the ability to determine the passage from one material to another.
Several devices that use axial oscillations in drilling have already been proposed. For example, mention may be made of the device described in document EP 994 758. The latter describes a coupling between a tool holder and its driving mount which constitutes a suspending of the tool holder from the mount in such a way that it can produce self-sustaining axial oscillations such that the rate at which the tool penetrates the workpiece varies cyclically around a mean rate which is of course non-zero.
Another document, DE 103 43 682, discloses a milling or drilling tool in which the rotary tool is subjected to a reciprocating axial movement by means of a piezoelectric or magnetic actuator housed in the tool holder, connected wirelessly to a power supply. The system is controlled remotely. This tool is intended for machining composite materials at very high (ultrasonic) frequencies and very low amplitudes of axial vibration.
Another document, US2008/041604, discloses a tool with an oscillating head in which the rotary tool is subjected to very high frequency oscillations which frequencies have to be equal to the natural frequency of the tool, so that the oscillation generated causes the tool to resonate axially. The actuators in the solutions described in document US2008/041604 are fully incorporated into the axial moving part of the devices, being incapable of generating movements and static or low-frequency loads at amplitudes high enough to break up the chips. In addition, because they involve the use of resonance, the characteristics of the oscillations obtained are very much dependent on the load, that is to say on the penetration force encountered during the machining operation.